1. Field of the Invention
The present invention relates to a method for detecting a malfunction in clamping a work within a machine tool and a machine tool performing the same.
2. Description of Related Art
In a grinding machine which grinds a work having a relatively elongated shaft-like shape, such as a crankshaft, both ends of a work are clamped by clamping mechanisms provided on a right-and-left pair of head stocks, and the work is machined while synchronously rotating main spindles of the pair of headstocks by servomotors as described in Japanese Patent Unexamined Publication JP-A-2002-239873. The clamping mechanisms use hydraulic chucks which chuck the work from the outer periphery of the work by chucking pawls driven by hydraulic chuck cylinders. The verification whether these clamping mechanisms have or have not properly clamped the work has been performed by using a pressure switch to check whether a specified pressure of operation fluid supplied to the chuck cylinder has been reached or not.
However, when there is abnormality in the driving mechanism of the chuck pawl, such as poor functioning of chuck pawl due to chips entering into sliding sections of the chucking pawls, the chuck pawl does not clamp the work at a predetermined clamping force although the pressure of the operation fluid supplied to the chuck cylinder is normal. If the grinding operation starts in this state, the work may slip in the chuck due to grinding force, thereby to cause a grinding failure. Furthermore, when the chucking pawls are used while in a state that they have contaminants adhered thereon, or in a worn-out state, similarly, the work may slip to cause a grinding failure. That is, the detection of only the pressure of the hydraulic oil supplied to the chuck cylinder may not always detect clamp malfunction.